Abstract 3005: Low-density lipoprotein receptor-related protein 1B (LRP1B) depletion promotes tumorigenicity by modulating fibroblasts in the tumor microenvironment in esophageal squamous cell carcinoma

Abstract Background: Esophageal squamous cell carcinoma (ESCC) is widespread worldwide with a poor survival rate. Tumor cells shedding from tumor tissues traveling to other organs through the blood circulatory system are called circulating tumor cells (CTCs). The CTCs in the blood of ESCC patients were enriched and then subjected to CTC mutational profiling by target sequencing. Our results suggested that CTC mutations in low-density lipoprotein receptor-related protein 1B (LRP1B) may have a potential prognostic role for ESCC. LRP1B belongs to the low-density receptor (LDLR) family with diverse roles in cellular functions and development, but the function of LRP1B in ESCC remains unclear. Therefore, this study aims to do a functional characterization of LRP1B. Methods: The CRISPR cas9 system was used to functionally knock down the candidate gene in ESCC cell lines with the highest endogenous level of LRP1B. The in vitro cell proliferation rate and viability were measured by MTT assay, colony formation assay, and wound healing assay. The in vivo tumorigenicity assay was performed to evaluate the tumor suppressive effect by subcutaneous injection. To examine the clinical relevance of LRP1B, we also performed immunohistochemistry (IHC) in tumor tissue microarray (TMA). Results: The reduction or loss of LRP1B mRNA was demonstrated in 60% of a panel of 15 ESCC cell lines. The depletion of LRP1B did not influence cell proliferation, cell clonogenic ability, or cell migration in ECSS cell lines. However, LRP1B depletion significantly promoted the growth of tumors in mouse xenograft models. Therefore, we hypothesize that LRP1B may be involved in modulating the tumor microenvironment (TME) by impacting various stromal components leading to an immuno-suppressive TME. We utilized RT-qPCR to investigate markers of various stromal components and observed that fibroblast markers (acta2, pdgfrb, and vimentin) had significantly higher expression levels after LRP1B downregulation in ESCC cell-derived mouse xenografts. The higher level of fibroblast cells was then verified by IHC staining. Further molecular mechanistic studies are underway and are expected to provide novel therapeutic insights by targeting the LRP1B genes. The LRP1B ESCC TMA data analysis is underway and statistical analysis will be presented. Conclusions: LRP1B plays a tumor-suppressive role in ESCC by modulating the tumor-associated fibroblasts in the TME. Acknowledgements: TBRS grant T12-701/17R and HMRF grant 05160926 to MLL Citation Format: KaiYan Xu, Josephine Mun-yee KO, Valen Zhuo you Yu, Maria Li LUNG. Low-density lipoprotein receptor-related protein 1B (LRP1B) depletion promotes tumorigenicity by modulating fibroblasts in the tumor microenvironment in esophageal squamous cell carcinoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 3005.